Ion implantation is a standard technique for introducing conductivity-altering impurities into a workpiece. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beams is directed at the surface of the workpiece. The energetic ions in the beam penetrate into the bulk of the workpiece material and are embedded into the lattice of the workpiece material to form an implanted region.
Solar cells are one example of a device that uses silicon workpieces. Any reduced cost to the manufacture or production of high-performance solar cells or any efficiency improvement to high-performance solar cells would have a positive impact on the implementation of solar cells worldwide. This will enable the wider availability of this clean energy technology.
Photoresist may be used to block ions that are implanted into a workpiece, such as a solar cell. However, adding and removing photoresist adds additional process steps and extra costs to solar cell manufacturing. Shadow or stencil masks held on or above a workpiece may be used to implant various patterns without additional process steps, which may increase throughput and decrease cost for solar cell manufacturing. However, a single shadow or stencil mask is limited in the shape or pattern of the possible selective implants. More complex patterns of apertures, such as those that can be formed using photoresist on a workpiece, cannot be manufactured in a single shadow or stencil mask. Accordingly, what is needed is an improved method and apparatus to process workpieces and, more particularly, an improved method and apparatus to form independent features on a workpiece, such as a solar cell.